description = [[
Retrieves or sets the ready message on printers that support the Printer
Job Language. This includes most PostScript printers that listen on port
9100. Without an argument, displays the current ready message. With the
<code>pjl_ready_message</code> script argument, displays the old ready
message and changes it to the message given.
]]

---
-- @arg pjl_ready_message Ready message to display.
-- @output
-- 9100/tcp open  jetdirect
-- |_ pjl-ready-message: "READY" changed to "p0wn3d pr1nt3r"
-- @usage
-- nmap --script=pjl-ready-message.nse \
--   --script-args='pjl_ready_message="your message here"'

author = "Aaron Leininger" 

license = "Same as Nmap--See http://nmap.org/book/man-legal.html"

categories = {"intrusive"}

require "nmap"
require "shortport"
portrule = shortport.port_or_service(9100, "jetdirect")

local function parse_response(response)
	local msg
	local line
	
	for line in response:gmatch(".-\n") do
		msg = line:match("^DISPLAY=\"(.*)\"")
		if msg then
			return msg
		end
	end
end

action = function(host, port)

	local status		--to be used to grab the existing status of the display screen before changing it. 
	local newstatus		--used to repoll the printer after setting the display to check that the probe worked.
	local statusmsg		--stores the PJL command to get the printer's status
	local response		--stores the response sent over the network from the printer by the PJL status command
	
	statusmsg="@PJL INFO STATUS\n"
	
	local rdymsg=""			--string containing text to send to the printer. 
	local rdymsgarg=""		--will contain the argument from the command line if one exists

	local socket = nmap.new_socket()
	socket:set_timeout(15000)
	try = nmap.new_try(function() socket:close() end)
	try(socket:connect(host, port))
	try(socket:send(statusmsg))		--this block gets the current display status
	response,data=socket:receive()  
	if not response then			--send an initial probe. If no response, send nothing further. 
		socket:close()
		if nmap.verbosity() > 0 then
			return "No response from printer: "..data
		else
			return nil
		end
	end

	status = parse_response(data)
	if not status then
		if nmap.verbosity() > 0 then
			return "Error reading printer response: "..data
		else
			return nil
		end
	end

	rdymsgarg = nmap.registry.args.pjl_ready_message
	if not rdymsgarg then
		if status then
			return "\""..status.."\"" 
		else
			return nil
		end
	end
	
	rdymsg="@PJL RDYMSG DISPLAY = \""..rdymsgarg.."\"\r\n"
	try(socket:send(rdymsg)) 		--actually set the display message here.
	
	try(socket:send(statusmsg))		--this block gets the status again for comparison
	response,data=socket:receive()
	if not response then
		socket:close()
		return "\""..status.."\""
	end
	newstatus=parse_response(data)
	if not newstatus then
		socket:close()
		return "\""..status.."\""
	end
	
	socket:close()
	
	return "\""..status.."\" changed to \""..newstatus.."\""
end
